A lash adjuster of the pre-cited type is disclosed in DE 199 42 983 A1. This lash adjuster is configured as a hydraulic support element for a finger lever of a valve train of an internal combustion engine. If the cam acting on the finger lever is in a lift phase when the internal combustion engine is shut off, the pressure piston sinks onto the opposing front end of the housing.
As is unnecessary to explain to a person skilled in the art, undesired particles can accumulate in the high pressure chamber. These consist, for example, of fabrication-related primary dirt or particles such as scuffing chips transported by the hydraulic medium. These particles form an adhesive deposit on the outer peripheral surface of the pressure piston and, at the next lash adjustment when the pressure piston executes an outward axial movement out of the bore of the housing, they can penetrate into a leak gap between the outer peripheral surface of the pressure piston and the bore of the housing. This can lead to a clamping of the pressure piston in the bore of the housing with the consequence that a lash adjusting function of the lash adjuster is no longer possible, or a proper valve lift can no longer be executed. The tendency of the undesired particles to form a deposit is promoted by the fact that a relatively small volume is available on the outer peripheral surface of the sunk pressure piston in the radial direction towards the annular enlargement (undercut).
Efforts have also been made in the prior art to solve the aforesaid problem with the primary dirt by using very complex rinsing measures. It is also known to prevent the ingress of undesired particles into the high pressure chamber using separators such as screens, magnets etc. arranged immediately upstream of the actual lash adjuster.